1. Field of the Invention
The present invention relates to a method and package for storing a pressurized container containing a drug.
2. Description of the Background Art
For environmental reasons, there has been a move to replace chlorofluorocarbons (CFCs) (also simply known as "fluorocarbons") such as P11, P114 and P12 with hydrofluoroalkane propellants such as HFA-134a and HFA-227. When these hydrofluoroalkane propellants are used as a propellant in a pressurized drug delivery system, various technical problems can occur with various drug formulations. Also, it is necessary to modify the construction of metered dose inhalers for optimum stability and aerosol formation.
One storing mechanism for a metered dose inhaler (MDI) uses a plastic tube which has a resealable lid to close the tube. The resealable lid for this tube employs a desiccant to absorb moisture present in the tube.
Such plastic tubes typically increase manufacturing cost and require complex and/or expensive manufacturing processes. Such tubes are frequently bulky in that they require a significant amount of storage space relative to the size of the container disposed within the plastic tube.
It is well established that non-CFC propellants, especially HFC 134a, have a much greater water solubility than the CFC propellants traditionally used in MDI'S. The maximum water solubility in HFC 134a is about 2200 ppm whereas for CFC 11, 12 and 114, the maximum water solubilities are about 130 ppm. (See Pischfiak, A. (1999) "Solvay Fluor and Derivate Chemical Data Sheet for CFC and; HFC Propellants.")
This maximum solubility may be further increased if cosolvents such as ethanol are used in the formulation. The mechanism of moisture transport into HFC MDI's has been discussed by Williams, G. and Toherevatchenkoff, A. (1999) "Moisture Transport into HFA-Free MRI's, " Respiratory Drug Delivery VI, Hilton Head, S.C., USA.
They concluded that moisture transport is influenced by the elastomeric nature of the valve gaskets as well as the type of HFA formulation and storage conditions employed. It may be appropriate, under certain circumstances to control the ingress of moisture into HFC based MDI's. A good example of this would be with a hygroscopic drug substance. Hence, prevention of moisture ingress is the subject of the invention whereby a series of secondary packageing embodiments demonstrate advantageously reducing moisture ingress.